1. Field of the Invention
This invention relates to a heat developable photosensitive composition containing an organic silver salt and a heat developable photosensitive member having a layer comprising the composition.
2. Description of the Prior Art
Photosensitive materials for forming silver images have been widely used and can give high quality of images which can be formed at high sensitivity. As the materials for forming silver images, there are usually known materials including organic silver salts as well as conventional silver halide emulsion. The silver image forming heat developable photosensitive materials including organic silver salts can be developed by a heat treatment alone after imagewise exposure. These silver image forming heat developable photosensitive materials can easily form images, in particular, the images can be formed by a dry process, and therefore, these materials have various advantages different from those resulting from conventional silver halide emulsions of a wet developing type and are expected to have wide application fields.
Such heat developable photosensitive material comprising an organic silver salt contains an organic silver salt and a halide as its essential components. The image formation is carried out by imagewise exposure of the heat developable photosensitive material and then heat development. In detail, the imagewise exposure causes a photochemical reaction of the halide with the organic silver salt to isolate a small amount of silver resulting in the formation of a latent image, and the small amount of silver thus isolated can be nucleus for developing the silver isolated from the organic silver salt by the subsequent developing procedure to produce a silver image at the exposed portions and thus complete the formation of a visible image.
These heat developable photosensitive materials comprising an organic silver salt usually do not have a high sensitivity because the materials are not mainly composed of a photosensitive substance of high sensitivity as in case of conventional silver halide emulsions, and further the original photosensitive composition remains at the non-exposed portion without subjecting to any change and therefore, isolation of silver at the non-exposed portion (non-image portion) is observed upon heat development, and it is very difficult to produce images of so high contrast as in case of a silver halide emulsion. In addition, even after the formation of images (silver images), the non-exposed portions have the same composition as that of the original (before exposure) photosensitive composition, and therefore, isolation of silver from the remaining organic silver salt is observed. In fact, fogging phenomenon is observed after the formation of images. Consequently, it is not possible to maintain the image quality (particularly, contrast) obtained upon the image formation, and the image stability is not sufficiently high.